This invention relates to a tubular frame member. More particularly, it relates to a joint end portion of a tubular frame member used as a part of a vehicle body frame structure of a motorcycle, which is to be jointed with another member.
There are known various joint portions, particularly weld-joint portions of tubular members which form a part of a vehicle body frame structure of a motorcycle. Examples of such frame members are disclosed in Japanese utility model publication No. 49-4428, Japanese early laid-open utility model publication No. 53-128653 and Japanese utility model publication No. 56-48631.
A weld-joint portion of a frame of the Japanese utility model publication No. 49-4428, as shown in FIG. 11, has a weld-joint portion 01A of a saddle pipe 01 which is formed of a round-pipe crushed so as to be jointed with a main pipe 02 and a weld-joint portion 03A of a supporting pipe 03 which is also formed of a round pipe crushed so as to be jointed with the main pipe 02.
A weld-joint portion of a sub-tube on which a seat is placed of the Japanese early laid-open utility model publication No. 53-128653, as shown in FIG. 12, comprises a plate portion 04A formed of a sub-tube 04 crushed and a rib 04B formed on the widthwise central portion of the plate portion 04A. A weld-joint portion of a frame of the Japanese utility model publication No. 56-48631, as shown in FIG. 13, is constituted as such that a weld-joint portion 06A of a rear upper pipe 06 to be welded to a main pipe 05, a weld-joint portion 07A of a center pipe 07 and a weld-joint portion 08A of a rear lower pipe 08 to be welded to a down tube 09 are all formed of a pipe material crushed and are wider than the diameters of the respective pipes.
There is also known a vehicle body frame structure as shown in FIG. 14 for example, in which a main frame 011 connected with a head pipe 010 is connected with a seat rail frame 012 and a sub-frame 013 and tightened by bolts 014 respectively and a lower end portion of a down tube 015 connected with a head pipe 010 is secured to a lower part of a main frame 011 by bolt 014.
The structure of the joint end portions of these frames 012, 013 and 015 to be jointed with other members is as such that, as shown in FIG. 15, a joint member 016 is engaged with a pipe hole and fixed therein by welding means 017 or otherwise, as shown in FIG. 16, an inner pipe 018 is fitted into a pipe hole, and the end portion thereof is crushed and such crushed end portion is formed with a bolt hole 019, and, in addition, a hole 020 for withdrawing a liquid for painting within the pipe hole is formed on the pipe.
However, the conventional tubular frame members with one ends crushed as shown in FIGS. 12 through 14 have a disadvantage in that the rigidity of the joint end portions becomes weak compared with that of the pipe portions due to the fact that their thicknesses are no more than twice of the thickness of tubular materials.
Another disadvantage of the above conventional tubular frame members is as follows. The joint end portion becomes extremely wide compared with that of the diameter of the pipe. Therefore, when this wide portion is abutted against the peripheral surface of the main pipe 02 of FIG. 11 for example and welded, the contacting surface of the joint end portion is required to be so worked as to curve along the peripheral surface and the welding area becomes vast. Particularly, when a square-shaped frame member is employed, the joint end portion becomes extremely wide. For example, when the square pipe member has a regular square shape in section, the width of the compressed joint end portion becomes two times as wide as the width of one side of the pipe member. Therefore, the welding workability and outer appearance become poor and thus undesirable. Moreover, since the difference in thickness between the compressed joint end portion and the square pipe is large, there arises a problem in that the joint end portion is required to be made long enough in order to weld the joint end portion along the peripheral surface of the member it is to be connected with.
When the compressed joint portion is formed with a bolt hole 019 as shown in FIG. 16, it is difficult to form, for example, an internal thread in the bolt hole 019 since the joint end portion is thin and therefore the inner pipe 018 is required to be fitted therein, thus resulting in an increase in the required working steps and parts.
On the other hand, the conventional tubular frame member of FIG. 15 in which the joint member 016 is welded to the tubular end portion requires an increased number of parts. In addition, a working step for welding 017 applied to the contacting portion between the tubular frame member and the joint member 016 is required, which again results in higher cost.